A city cop who testified he was seduced at age 13 by his East Side Montessori school principal suffered a figurative beating by the same headmistress in court yesterday.

Under cross-examination in Manhattan Supreme Court, by the defense lawyer for Lina Sinha, 40, the cop repeatedly could not remember specifics about the alleged statutory oral sex and rapes, the earliest of which happened at the East 55th Street school 11 years ago.

“The guy is testifying about things that happened 10 years ago,” responded the trial judge, Justice Carol Berkman. “The question could be asked, ‘Could you pass such a test?’ ”

Particularly damning was when the cop – a now-24-year-old patrolman whose name is being withheld due to the sexual nature of the charges – was caught in a contradiction.

On Friday, he’d testified that Sinha engaged in intercourse with him for the first time as a 15th-birthday present. Shargel reminded him that he’d, instead, told a detective that he was 16 when the principal took his virginity.

Shargel also tried to portray as implausible the boy’s account of repeatedly sneaking into Sinha’s bedroom in high school for weekend-long trysts – just down the hall from Sinha’s mother’s bedroom.

“Did that involve any noise?” Shargel asked. “Noises that are often attendant to the act of making love?” The cop answered, “The TV would be on loud.”